The log cabin idea is a good one. I saw a crib quilt recently in grey and white gingham, white and citrus yellow which looked fabulous. It was very simple with the gingham used for an appliqued shape and the name of the baby, plus one border and the bright colour also used as an internal border.
An Amish type of quilt used black as a thin border around colored squares and as links between the squares with a strong blue as a sashing; that was interesting too.
Babies like looking at geometric patterns and black, white and gray can be an exciting combination so I wouldn't worry about it not being a traditional combination. All the quilts I have made for babies in our family have been used as play mats anyway as small babies often don't have quilts in their cribs.
You can get good ideas about what modern mothers like by going online to the upscale baby store sites and seeing what the current top sellers are.
Good luck with whatever you choose to make.
Suzan (Maine)